1. Field of the Invention
The present invention relates to an image processing technique for processing images captured by an X-ray image diagnostic apparatus.
2. Description of the Related Art
Imaging systems using photomultipliers as X-ray detection units have hitherto been widely utilized as X-ray image diagnostic apparatuses for making medical diagnoses. Such imaging systems, in which a captured image that has undergone phototransformation in such a photomultiplier is processed in analog form and displayed in a monitor, are called “analog image intensifiers”.
However, X-ray image diagnostic apparatuses utilizing digital X-ray imaging systems that digitally detect X-rays and form captured images (called “digital X-ray image diagnostic apparatuses” hereinafter) are becoming more common as of late, taking the place of such analog image intensifiers.
An apparatus that uses a flat panel detector (abbreviated as “FPD” hereinafter) as its detection device can be given as a representative example of a digital X-ray image diagnostic apparatus.
FPDs are provided with units configured of, for example, solid-state image sensors having high X-ray sensitivity that convert detected X-rays into electrical signals based on their intensity, and output the electrical signals. Alternatively, the FPDs are provided with units that combine a scintillator, which absorbs the energy of the X-rays and emits fluorescent light of an intensity in accordance therewith, with a photoelectric conversion element, which has a high sensitivity to visible light and converts that light into electrical signals based on the intensity thereof. The FPDs are provided with such units as well as A/D converters that digitize the analog signals from those units.
Digital X-ray image diagnostic apparatuses that use such FPDs are capable of realizing wider dynamic ranges and obtaining higher-resolution images than X-ray image diagnostic apparatuses that use conventional analog image intensifiers. Recently, digital X-ray image diagnostic apparatuses are also showing properties that are not inferior to conventional image intensifiers in terms of frame rates when capturing moving pictures.
Furthermore, because digital X-ray image diagnostic apparatuses enable the captured images to be handled in digital form, they allow more advanced image processing to be performed, without drops in image quality during processing, transmission, and storage.
The spread of digital X-ray image diagnostic apparatuses can therefore contribute to improvements in the accuracy of diagnoses due to the higher image quality. Such apparatuses can also contribute to the implementation of new types of medical systems, such as data management facilitated by the digital nature of the images, links with other medical devices through digital networking, and so on.
Recently, remote medical services are garnering attention as one such new medical system.
In the past, it has been difficult to perform emergency medical procedures, perform examinations and treat problems using advanced devices, and so on in regions that are unable to obtain specialized medical care, such as remote islands that lack general hospitals. Therefore, when emergency medical care is necessary in such regions, doctors working outside of their specialization generally provide the initial care, after which the patient is transported to a general hospital capable of more advanced medical care. However, it often takes time to select the hospital to transport the patient to, and to actually transport the patient to that hospital.
In light of this, if a communication path capable of transferring data between clinics on remote island and general hospitals in larger cities could be laid and remote medical services provided, captured images obtained using an X-ray image diagnostic apparatus on the island could be viewed by specialists in a general hospital.
Implementing remote medical services using such an X-ray image diagnosis system makes it possible to obtain high-level examination/treatment services under the instruction of a specialist even in regions that lack advanced medical facilities.
It goes without saying that when implementing such a remote medical service, it is necessary for the transmitted captured images to be of a quality sufficient for diagnosis and treatment, and it is particularly necessary, in terms of diagnostic performance, for the image resolution to be sufficiently high. At the same time, it is particularly necessary, when making diagnoses and performing treatment using moving pictures, to ensure a frame rate sufficient for making diagnostic and treatment instructions.
However, there are often constraints on the transmission bandwidth that can actually be used, and in light of this, it is necessary to efficiently encode captured images in order to reduce the data amount thereof before transmitting the images. However, because the captured images are used for diagnoses and treatment, excessive compression coding leading to a drop in image quality is unacceptable.
Therefore, when implementing such a remote medical service, it is important to efficiently transmit captured images of the required quality within the effective bandwidth for transmission (in other words, to implement efficient transmission while also maintaining high-resolution image quality).
Selectively changing the method used to encode the captured images is useful as a way to implement efficient transmission while also maintaining high-resolution image quality in such a manner. Japanese Patent Laid-Open Nos. 06-209926 and 01-189772 (hereinafter referred to as Patent Documents 1 and 2 respectively) are known as techniques for selectively changing the method used to encode captured images.
Patent Document 1 discloses a configuration that changes the amount of data obtained (frame rate, X-ray amount) and the compression coding method depending on whether a region is a specified region of interest or not. Patent Document 2, meanwhile, discloses a configuration that detects biological changes and changes the compression coding method based on the detected changes. In Patent Document 2, frames considered more important in terms of biological changes are encoded using a lossless compression method, whereas other frames are encoded efficiently using a lossy compression method.
However, the configurations disclosed in Patent Documents 1 and 2 are not intended to implement remote medical services, and do not aim to control encoding captured images within the effective bandwidth for transmission. Therefore, applying such configurations as-is to a remote medical service may result in the data amount exceeding the effective bandwidth for transmission.
To be more specific, with Patent Document 1, the effects of the compression coding are reliable when parts necessary for diagnosis and parts unnecessary for diagnosis coexist within the same frame. However, this technique is ineffective when, for example, irradiating only an area of interest with X-rays and not imaging the other areas in order to reduce the amount of X-ray irradiation as much as possible, as with radioscopy imaging.
Meanwhile, Patent Document 2 changes the compression coding method based on time, as opposed to Patent Document 1, which changes the compression coding method based on space; thus a certain degree of effectiveness can be expected. However, because the data amount depends on biological changes, there is no guarantee that that data amount will fall within the effective bandwidth for transmission.